ASTM A193 B7 vs B8 Bolts: What’s the Difference and Which One Should You Use?

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ASTM A193 B7 vs B8 Bolts: What’s the Difference and Which One Should You Use?

15/04/2026

🔷 What are ASTM A193 B7 and B8 bolts?

ASTM A193 is an international standard specification for bolts and stud bolts used in high-pressure and high-temperature applications, such as flanges, valves, and piping systems.

The two most commonly used grades are:

B7 (alloy steel – Chrome Moly steel)
B8 (stainless steel – mainly 304/304L)

👉 These two grades have very different properties and applications.

⚙️ What is an ASTM A193 B7 bolt?

A B7 bolt is made from chromium-molybdenum alloy steel (Cr-Mo steel).

📌 Key features:

High tensile strength (~860 MPa or higher)
Excellent high-temperature resistance
Suitable for high-pressure applications
Can be coated (e.g., zinc plating)

👉 Commonly used in high-pressure and high-temperature systems

⚙️ What is an ASTM A193 B8 bolt?

A B8 bolt is made from stainless steel (typically 304 or 304L).

📌 Key features:

Excellent corrosion resistance
Lower mechanical strength than B7
Suitable for chemical environments
Not suitable for very high temperatures

👉 Commonly used in corrosive environments

📊 Comparison: ASTM A193 B7 vs B8

Criteria	B7 (Carbon Alloy Steel)	B8 (Stainless Steel)
Material	Cr-Mo alloy steel	Stainless steel 304/304L
Strength	Very high	Medium
Temperature resistance	High	Medium
Corrosion resistance	Low	Excellent
Applications	High-pressure systems	Chemical & corrosive systems
Cost	Lower	Higher

🏭 When should you use B7 bolts?

Choose ASTM A193 B7 bolts when:

✔️ High-pressure systems

Oil & gas
Steam systems
Power plants

✔️ High-temperature conditions

✔️ Flange and heavy industrial applications

🏭 When should you use B8 bolts?

Choose ASTM A193 B8 bolts when:

✔️ Corrosive environments

Chemical processing
Seawater applications

✔️ Anti-corrosion requirements

✔️ Medium-pressure systems

⚠️ Common mistakes

Using B8 bolts in high-pressure systems → risk of deformation and failure
Using B7 bolts in highly corrosive environments → corrosion issues
Ignoring temperature and working conditions

🔥 Quick selection tips

👉 High pressure & high temperature → choose B7
👉 Corrosion resistance → choose B8

🏁 Conclusion

ASTM A193 B7 and B8 bolts are designed for different applications:

B7 = high strength and high-pressure resistance
B8 = excellent corrosion resistance

👉 Choosing the right bolt helps:

Improve system safety
Extend equipment lifespan
Reduce maintenance costs

📞 Contact Information

Phuc Minh Engineering Co., Ltd (PM-E) specializes in supplying bolts, valves, and piping components that meet international standards.

🌐 Website: pm-e.vn
📧 Email: info@pm-e.vn
📱 Hotline: +84 907 450 506 – +84 902 720 814 - +84 979 737 351

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